Naturally occurring coals and artificial chars are under intensive study becausethey can be used as sensitive electron paramagnetic resonance (EPR) probes for paramagnetic gases dissolved in tissue. We have studied the magnetic susceptibility of these materials by using two techniques - EPR and SQUID. While the SQUID measurements provide an average of the susceptibilities of all paramagnetic states in the sample, the EPR measurements reflect mainly the part which corresponds to the spin system with high exchange interaction. The Weiss constant and exchange integral were evaluated from the SQUID susceptibility experiments and compared with the EPR data. Evidence of two spin systems with relatively high and low exchange interaction was obtained.